1. Field of the Disclosure
The present disclosure relates to a white light emitting device (LED), and more particularly, to a white LED having an improved structure for higher light emission efficiency.
2. Description of the Related Art
As the light emitting efficiency of nitride semiconductor based blue and green light emitting devices (LEDs) and red LEDs using InGaAIP has increased, attempts to use such LEDs as lighting device beyond the current wide use for displays are expanding worldwide. LED light sources have superior characteristics to conventional light sources, i.e., very small size, 10% less power consumption, 10 times longer life time, 1000 times faster reaction speed compared to other light sources. Moreover, LED light sources are environment friendly in that they do not emit harmful rays such as ultraviolet rays and do not use mercury or other discharging gases. Since the adoption of the Kyoto Protocol for preventing global warming in December 1997, attempts to reduce the amount of CO2 to 1990 levels by 2010 are spreading worldwide, and many countries, including Japan and the U.S.A., put forth much energy into the reduction of energy consumption. In this atmosphere, LEDs are becoming distinguished, next generation light sources and the LED-based lighting market is rapidly growing.
For use as general lighting sources, first of all, white light can be obtained using LEDs. Methods of implementing white LEDs are categorized into three types. First, white light can be obtained by combining three—red, green, and blue—LEDs. This method requires the three LEDs to produce one white light source, and techniques of controlling each of the LEDs. Second, white light can be obtained by exciting a yellow phosphor using a blue LED. This method provides high emitting efficiency but leads to a low color rendering index (CRI). CRI is likely to vary according to the current density, thus much research is required in order to obtain white light that is close to solar light. Third, white light can be obtained by exciting red, green, and blue phosphors using ultraviolet (UV) LED. This method can be used in a high current condition and provides the color gamut of high quality. Therefore, this method has been most actively researched and developed. As described, to implement such a white LED, the three principle color phosphors composed of conventional inorganic phosphors can be used. However, such inorganic phosphors, especially red inorganic phosphor has low light emission efficiency, thus obstructing the implementation of highly efficient, high light emission, white LEDs.